The present invention relates to a method of traversing an advancing yarn during the winding of the yarn into a yarn package.
A method of this kind and an apparatus for traversing a yarn are known from EP 0 453 622 B1. In this known process, a traversing yarn guide is mounted on a belt of a belt drive. The belt drive is driven via a stepping motor in such a manner that the traversing yarn guide reciprocates the yarn within a traverse stroke. In the region of reversal, the stepping motor is supplied with a saturation current and in the remaining region with a rated current. The motions are controlled at a position within the traverse stroke by means of a sensor.
However, the known method is subject to physical and technical limitations. From the physical viewpoint, the stepping motor represents a spring-mass system, which is liable to vibrate in the case of rapid changes in position and to perform uncontrolled movements. During a movement of the yarn guide, the reference or zero position is passed only twice. The accuracy of positioning outside of the zero position is undefined. At higher rotational speeds, such as, for example, a production speed of 1,000 m/min., this method is no longer able to operate with the necessary accuracy.
It is therefore the object of the invention to create a method and apparatus for traversing a yarn, which permit an exact positioning of the yarn within the traverse stroke. A further object of the invention is to ensure an optimal utilization of the electric motor in each traverse stroke.
The above and other objects and advantages of the invention are achieved by the provision of a yarn winding method and apparatus wherein the yarn traversing mechanism includes at least one yarn guide, and means including an electric motor for traversing the one yarn guide along the rotating winding spindle and so as to define a traverse stroke. A sensor is provided for continuously monitoring the actual position of the one yarn guide as it moves along the traverse stroke, and control means is provided for comparing the monitored actual position of the one yarn guide with a predetermined desired position, and generating a control signal in response to a difference between the monitored actual position of the one yarn guide and the predetermined desired position so as to control the operation of the electric motor. The yarn is thereby accurately positioned along the entire traverse stroke in accordance with a predetermined winding program.
The invention as summarized above is not suggested by EP 0 302 461. In the traversing apparatus of that document, a plurality of traversing yarn guides are mounted one after the other on a belt and are driven by means of a servomotor. This servomotor is commuted by means of a resolver, so as to be reversed according to a predetermined desired function. The position of the traversing yarn guide is not detected. The known traversing apparatus, which is used at production speeds from 150 to 170 m/min., is totally unsuited for reciprocating a yarn at traversing speeds up to 7 m/sec. due to its high mass moment of inertia.
However, the method of the present invention facilitates such a highly dynamic movement of the traversing yarn guide without difficulties. The special advantage of the invention lies in that a constant adjustment occurs between the actual position and the desired position of the traversing yarn guide. A measuring device coupled with the traversing apparatus offers the possibility of utilizing the full dynamics and the full moment of the electric motor, without incurring the risk that the motor falls out of step. Primarily, this generates a high accuracy and reproducibility in the outer ranges of the movement of the traversing yarn guide, namely in the region of the reversal at the outer edge of the yarn package, while the yarn is being traversed.
In the event of a deviation between the actual position and the desired position, a differential signal is generated for controlling the electric motor. In this instance, the setting of the electric motor is understood to be the relation between the movable rotor and the stationary stator of the electric motor. Thus, it is made possible to move the traversing yarn guide in a position-controlled manner over the entire traverse stroke. As a result of the continuous adjustment between the actual position of the traversing yarn guide and the desired position of the traversing yarn guide which is determined by the electric motor, the electric motor is in a position to exactly apply the energy or torque that is required for every position of the traversing yarn guide.
The special advantage of the invention lies in that the electric motor is controllable in an amplitude-controlled manner. This means, that in case of a deviation between the actual and the desired position, the electric motor will receive by means of the differential signal a current that is varied in its amplitude. In particular, this allows a high accuracy to be realized for the positioning of the traversing yarn guide in the reversal region.
In a further, advantageous variant of the method, the differential signal is also used to change the rotational speed of the electric motor. This allows to adjust the speed of the traversing yarn guide by the frequency-controlled motor in every position within the traverse stroke to a predetermined sequence, so that the laws of winding can be put into action with a high accuracy during the formation of packages. For example, random winds, precision winds, or conical packages can be realized with corresponding speed profiles and with a high accuracy. The traversing speed is in a range of about 800 double strokes per minute.
In this connection, it will be especially advantageous, when for each kind of wind a respective course of the desired position of the traversing yarn guide is predetermined within a traverse stroke for controlling the electric motor. The course of the desired position of the yarn guide predetermines the position and the speed of the traversing yarn guide. With that, the method is suitable for carrying out stroke reductions. The stroke reductions may be varied as desired on one side or on both sides according to a predetermined time program.
To be able to wind yarn reserves as precisely as possible at the beginning of a winding cycle, it will be advantageous, when at the beginning of the winding cycle, an adjustment is made between the position of the traversing yarn guide and the setting of the electric motor with the aid of a reference position.
Especially advantageous is the variant of the method, wherein the reference position is defined by one of the ends of a tube that receives the package. With that, it is ensured that despite differently long tubes, the available winding length of the tube corresponds in each instance exactly to the traverse stroke.
The method of the present invention offers the possibility of detecting the actual position of the traversing yarn guide by a sensor that is optically, acoustically, or electrically coupled with a measuring device. In the case of an optical detection, for example, lasers are used, which detect the position of the yarn guide by way of measuring the distance.
However, it is also possible to use ultrasound sensors for measuring the actual position of the yarn guide.
In a particularly advantageous variant of the method, wherein the yarn guide is moved by means of a belt drive, the sensor of the measuring device is connected to the motor shaft of the electric motor, which drives a drive pulley of the belt drive.
When using this variant, it is possible to detect the angle of rotation or the number of revolutions of the motor shaft, which corresponds, based on the transmission mechanism, to the respective actual position of the yarn guide.
Especially advantageous is the variant of the method, wherein the sensor is arranged on one of the belt pulleys, and determines an angle of rotation or the number of revolutions of the belt pulley.
Basically, the method of the present invention can be applied to any kind of drive of the traversing yarn guide. The variant of the method, wherein the traversing yarn guide is driven by means of a stepping motor is especially of advantage because of its high flexibility. Likewise, the low moments of inertia of the stepping motors make it possible to impart a high torque, which is necessary especially in the reversal regions of the traversing yarn guide.
The method of the present invention may be carried out both with a traversing apparatus, wherein the traversing yarn guide is reciprocated within a traverse stroke, and with a traversing apparatus, wherein two oppositely driven traversing yarn guides are moved within a traversing stroke. The traversing apparatus of the present invention distinguishes itself in particular by a reproducibility of the yarn deposit on the package as well as by its high flexibility with respect to the package build.
A particularly advantageous further development of the traversing apparatus provides that a plurality of traversing yarn guides are provided for reciprocating a plurality of yarns in winding positions arranged parallel to one another. In this arrangement, the traversing yarn guides moving in the same direction are driven by an electric motor. However, for controlling the position and speed of the traversing yarn guides, the measuring device is associated to only one of the traversing yarn guides moving in the same direction. This configuration allows to control any desired number of parallel arranged winding positions of a machine.
To attain a high accuracy in the detection of the actual position of the traversing yarn guide, it is preferred to use the traversing apparatus, wherein a sensor of the measuring device is in contact with the traversing yarn guide.
With a use of a noncontacting sensor in a particularly preferred variant of the embodiment, the existing flexibility of the traversing apparatus is likewise further increased.
Thus, for purposes of determining the actual position of the traversing yarn guide, it is possible to use conventional sensors, such as optical laser sensors, acoustical ultrasound sensors, noncontacting magnetic or capacitive sensors, as well as electric rotation pickups.
Since due to constructional conditions the scanning of the traversing yarn guide is often confronted with difficulties, a traversing apparatus is especially advantageous, wherein the measuring device for detecting the actual position of the traversing yarn guide is coupled with one of the drive means that moves the traversing yarn guide.
In this connection, the traversing apparatus wherein the traversing yarn guide is guided by means of a belt drive, represents a variant, wherein the masses being moved are small, so that the electric motor is able to impart the torque necessary for the high speeds.
In this variant, the belt is guided over a belt pulley and drive pulley. The electric motor is coupled with the drive pulley, so that the rotation is transmitted to the belt. The belt may also be formed by a cable or another tapelike means.
The further development of the traversing apparatus, wherein the sensor of the measuring device covers a number of markings provided per length unit on the belt, has the advantage that it thus senses the direct transmitting member of the movement of the traversing yarn guide. In this instance, it is possible to use as markings, for example, the projections of a cog belt.
The embodiment of the traversing apparatus, wherein the sensor of the measuring device is arranged directly on the electric motor in such a manner as to detect the angular position of the number of revolutions of the motor shaft connected to the drive pulley, leads to a particularly compact design.
In addition, it is possible to configure the connection of the measuring device to the control device in such a manner that high transmission accuracies of the signals are attained. The adjustment between the actual position and the desired position of the traversing yarn guide can thus be balanced within very short regulating times, while minimizing disturbance influences.
In this connection, the drive of the traversing yarn guide by means of a stepping motor is especially advantageous. As a result of the large number of paired poles, for example, fifty poles, it is possible to adjust the desired position of the traversing yarn guide very accurately within the traverse stroke. The measuring device and the therewith connected control system permit elimination of vibrations as occur frequently with the stepping motor in quick reversal actions. As a result, the stepping motor can be utilized far better than is possible in mostly only controlled operations.